Voice frequency and direct current impulse repeating system



July 22, 1947. CfGlLLlNGS ET AL I 2,424,452

VOICE FREQUENCY AND DIRECT CURRENT IMPULSE REPEA'I'ING SYSTEM Filed Dec. 8, 1944 2 Sheets-Sheet l A VFT l --X- II --x Hp P2 0 I 1 5 f 13 INVENTORS CHARLES GlLLlNGsv CHARLES E. BEALE ATIORNEY Ju ly 22, 1947. c. GILLINGS ET AL 1 2,424,452

VOICE FREQUENCY AND DiRECT CURRENT IMPULSE REPEATING SYSTEM FiledDec. s, 1944 2 Shets-Sheet 2 EMMS M63 M1. H occz\ l -x-{I- 5 7 AA v2 2 i DCC T EMMZ INVENTORS vCHARLES GILLINGS CHARLES E.BEALE ATTOR NE Y patented July 22, 1947 VOICE FREQUENCY AND -DIREGT- CURRENT IMPULSEREPEAT-ING' SY STEM Charles 'Gi llings and Charles E'dinund Beale,

Liverpool, England, assignors "to Automatic Electric Laboratories, lnc.,6hicago, "111., a'corporation of Delaware Application December 8, 19,44,1SeriaLNo, 567,230 In Great Britain February 23, 1944 1 The present invention relates to telephone'ior like signalling systems and is moreiparticularly concerned with voice frequency dialling arrangements such as are employed'for the setting up of automatic telephone switching apparatus over 11 Claims. (Cl. 179-16) whether under operator or subscriber controL it has hitherto been considered necessary to provide in the outgoing equipment a one-way Voice repeater in order to prevent the'voice frequency receiver in the distant incoming equipment from being falsely operated by spurious frequencies such as may be generated by the calling, party talking or singingintothe microphonejpriorto or between the dialling of the various digits required for the setting up of the connection. The one-way repeater atthe-outgoing end will only allow of transmission in a backward direction, i. e., from the incoming to the outgoingferiilarid hence arrangements must be made-for .this repeater to be removed from the connection when conversational conditionsareestablished, an fend of selection orcalled subscriber answer signal being usually? utilised to institute its removal. This involves an undesirable operating. procedure in order to avoid charging the subscriber for service calls. 4

The-chief object of the presentinventionis .to

controlling the setting of automatic switches; in

order to reduce the risk. of false 1' operation by speech currents a train of direct current impulses is converted for "transmission over a voice .frequency'link into a train of voice frequency impulses the number of which differsin'a predetermined manner from the number of direct current impulses and the nature "of which is different for differently placed impulses in the train.

According to another feature of the .inventedjasiimpulsesof asingle?voice"frequency and a further impulse'of a plurality ofvoice frequencies isjfautomatically transmitted at the end'of the train.

,A further feature of the invention is that in an arrangementfor'convertinga train of voice freque'nc'y'l'impulses into direct "current impulses d'ifiering" innumber'therefrom, the equipment is adaptedjinresponseto a train of incoming impulses the first and last of'which comprise a plurality offrequencies while the remainder if any comprise asingle'frequency to'retransmit a number' of direct current impulses one less'than the numberof voicefre'quency impulses received.

'The invention will be betterunderstood from thefollowing description of one method ofcarrying'it into effect reference being had to the accompanying. drawings comprising I Figs. 1 and' 2 which show, parts of the circuits of a typical outgoing D. 1C./V. F. relay set and of an-incoming -V. F;/D.'C. relay set as modified for thepurpose or carrying out the invention.

Itwill be assumed for the purposeof the description-that the outgoing D. C./V. F. relay set oflFigfl-is accessible toga trunk operator in which case leads Ill and I I will connect with a switchboard jack at the operators positiomwhile leads Mandi [3 will connect With'theVJF. dialling and signalling trunk line. In Fig. 2 leads [4 and I5 connect with the distant incoming end of the trunk'linawhile leads l6 and I! connect with an incoming selector switch. In this relay set it will be necessarytoarrangefor the associated V.F. receiver (not shown) to respond to two differing voice frequencies which will be termed X and Y. The V.'F.' impulsessent out toline at; the out- "going end fortypicaldialled digits '1, '2 and 4, and the "D. C. impulses sent 'iorward fromi the incoming end in response to thereception of V. F. impulses, can'beiseen from the following table in which "XY represents a locally-generated compound V. F. pulse.

Digit Outgoing End Incoming End 'XY--'XY XYXY.absorbed l Locally generated D. C. im-

7 pulsesent. XY-X absorbed Xi repeated as D; C.-impulse. Locallygenerated D. 0. impulse sent. XYX-absorbed X repeated as D. C.impulse. X repeated as DZ 0. impulse. XYrepeatedas D: Cflimpulse. Locally generated D. O.'iIJ1- pulse sent.

As is usual, the 'D. 30. impulses will comprise periodicbreaks in a closedfD. C. loopcircuit while the corresponding V. .F.'.imp11lses will comprise 'pulsesiof tone in an ZODGHVQF. circuit.

Fromthe above table it will be seen that the V. F. relay set at the incoming end must receive a compound frequency impulse followed by either a compound or a single frequency impulse before,

any D. C. impulses can be sent out to the in coming selector switches.

tion, the lengths of such impulses and the spac- Furthermore as will i be appreciated from the ensuing circuit descriplay EM releases.

ing therebetween must bear a given relation to I Assuming now that the operator has plugged into the jack connecting with leads and II, when she throws her dialling key relay A is caused to operate and at contacts AI brings up relay B which prepares a circuit for relay EB at contacts BI.

When the first digit, for instance 4, of the required number is dialled, relay A responds and on the first break of the dial contacts relay A at contacts Al short-circuits relay B, and at the same time removes the short-circuit from relay EB which operates. tacts EBI prepares an operating circuit for relay EM, at EB2 completes a circuit for relay SP and at E133 and EB4 applies both X and Y voice frequency to the trunk via transformer VF'I and contacts SPI and SP2.

On the first make of the dial contacts, relay A in re-operating short-circuits relay EB and recompletes a circuit for relay B which was held by short-circuiting during the preceding break period, while at the same time anoperating circult is completed for relay EM. With relays EM and A operated the forward XY frequency pulse is terminated.

Relay A in releasing on the second dial break Relay EB in operating, at conperiod recompletes a circuit for relay EB, which was held by short-circuiting during the preceding make period, and short-circuits relay EM. At contacts A2 X frequency is now applied via transformer VFT to line.

On the second make, relay A in re-operating I quency impulse is sent forward in the manner already described, relay EB being energised on each break of A and being short-circuited on each make, while relay EM is energised on each .50 For each succeeding dialled impulse an X fremake of relay A and short-circuited'on each i break.

A range of dialling speeds of from 7-12 impulses per second is assumed, with a nominal break-to-make ratio of 2:1, so that the break periods will vary from 56 milli-seconds (m. s.) at 12 I. P. :S. to 96 m. s. at 7 I. P. S. and the make periods will vary from 28 m. s. to 48 m. s. Relays EB and EM are designed to release under shortcircuit conditions after periods of 50-75 m. s. and 100-150 in. s. respectively so that they will readily hold operated during each impulse train.

At the end of the dialled impulse train, relay A will remain operated and will maintain relays B and EM and will short-circuit relay EB, whereupon a supplementary impulse of XY frequency will be generated and sent out to line in the fol.- lowing manner. On the release of relay EB after its slow period, relay EM is short-circuited via resistance YA and contacts EB! under which condition it has a release lag of -90 s. With relay EM operated and EB normal, XY frequency is again applied to line and this persists until re- Relay EM in releasing opens the circuit of relay SP which releases slowly and relays A and B remain held in readiness for a further digit.

Referring now to Fig. 2, consideration will be given to the reception of the V. F. impulse train for dialled digit 4 which will comprise XYX-- X--XXY. It should be explained that in response to the usual seizing signal of X frequency relays BZ and NN (not shown) in the incoming equipment will have been operated from contacts of the V. F. receiver relay X (not shown), these relays remaining operated until such time as the final clear-down signal is subsequently transmitted by the distant outgoing operator. Relay BZ in operating, at contacts BZI and BZ2 energises relays DCC, CC and AA. Relay NN in operating, at its contacts NNI prepares the incoming selector switch for receiving a train of D. C. impulses by extending the earthed relay IL forward over'the negative lead i l to operate the selector impulsing relay on its upper winding.

In response to the first pulse of XY frequency the incoming V. F. receiver relays X and Y (not shown) both operate and at contacts XI and Yi open the circuit of relays DCC and CC. Relay CC holds due to its short-circuited second winding but relay DCC releases whereupon at contacts DCC2 and X2 relay AA is released and operates relay EBB over the following circuit: earth, contacts NN2, winding of relay EBB, contacts DZ2, AAI' and CCI to battery via resistnce YH.

At the end of the XY frequency pulse, relays X and Y release, whereupon relay DCC re-operates in series with relay CC which has held during reception of the signal due to its shortcircuited winding. Relay DCC in re-operating and relay X in releasing again bring up relay AA, whereupon relay EBB is short-circuited and relayi EMM is energised via operated contacts EBB]. On reception of the second X frequency pulse, relay X (not shown) again operates and at contacts X2 extends earth from BZ2 via contacts EMM2 and M3 to bring up relay MC. Contacts X2 also release relay AA, whereupon relay EB3'is energised and relay EMM is short-circuited via operated cont-acts EBB! Relay MC in operating, at contacts MCI brings up relay DZ and at contacts MC2 brings up relay SG. Relay DZ in operating locks independently of relay MC at contactsDZl and at contacts DZ2 completes a locking circuit for relay EBB. Relay SG in operating at contacts SGISG3 introduces resist- .ances YCYG into the speech transmission circuit,,these resistances constituting a bothway line termination with infinite .attenuation thus splitting the' line between the incoming and outgoing sides of the circuit so that any surges produced bythe selector impulsing relays during the subsequent setting up of the selectors will be prevented'from extending back to the V. F. trunk line and. interfering'with the proper operation of the echo-suppressors.

. At the termination of the X impulse, relay X releases and re-operates relay AA, whereupon relay EMMisagain energised. With relays EMM and MC operated, earth now extends over con- .tacts BZ2, X2, EMM3, MC3 and MI to bring up relay M and this relay locks over its contacts Ml, operates relayPD over contacts M2 and releases .IQIayMC at contacts M3. Relay PD in Operating maintains an alternative circuit for relay SG at contacts PDI, at contacts PD2 further disconnects the speech transmission circuitand at contacts PD3 replaces the forward holding earthto the selector impulsing relay by a holding loop via contacts AA2 and EBBZ' in readiness for the transmission of D. C. loop impulses to this relay.

On receipt of the second X pulse, relay X again operates, whereupon relay AA releases as before and short-circuits relay EMM at contacts AAI,

while contacts AAZ initiate the break period of the first output D. C. impulse.

At the end of the X impulse relay X releases and relay AA re-operates, whereuponrelay- EMM is held at contacts AA! and at contacts AAZ the output D. C. break period is terminated.

On reception of the third X pulse a further D. C. loop impulse is sent out in like manner.

When the final XY frequency impulse is received, relays X and Y are operated and relays DCC and AA are released, relay AA in releasing initiating the third D, C. break period. Relay AA in releasing also short-circuits relay EMM, While relay DCC in releasing releases relay DZ so that.

relay EBB now holds via normal contacts DZZ and AA! and operated contacts CCl to battery via resistance YH.

At the termination of the XY frequency impulse relays X and Y release, whereupon relays DCC and AA operate. Relay AA terminates the third output D. C. break period and short-circuits relay EBB and holds relay EMM. Since the XY frequency impulse terminates the V. F. train, relays DCC and AA will remain operated long enough to allow relay EBB to release and when this occurs, relay EMM is short-circuited and commences to release. On the release of relay EBB contacts EBBZ initiate the fourth output D. C break period, while contacts EBBS open the circuit of relay M which commences to release slowly. On the release of relay M after 60-90 m. s. the fourth output D. C. break period is terminated at contacts M5, while at contacts M2 relay PD is released and restores the outgoing circuit at contacts PD2 and PD3. Relay PD in releasing also" opens the circuit of relay SG at contacts PD! and when this relay releases after its slow period, which is sufficient to cover the hunting time of the selector and the switching through to a subsequent selector, the transmission circuit is restored to normal.

Relays BZ, NN, AA, DCC and. CC remain operated in readiness for subsequent trains of incoming V. F, impulses.

If the next digit dialled is 9, a V. F. impulse train comprising an XY pulse followed by eight X pulses and terminated by a further XY pulse which is locally generated at the outgoing end will be received at the incoming relay set. As in the case of digit 4 the initial XY pulse and the first X pulse will be absorbed, while the remaining seven X pulses will be converted into D. C. form. The final XY pulse will be also converted into D, 0. form and then a locally generatedDrC. impulse will be enerated to bring up the required total of nine impulses.

Assuming now that digit 1 is dialled, relay A in releasing at the outgoing end brings up relay EB in the usual manner and this relay in turn brings up relay SP, whereupon an XY frequency pulse is sent to line. On the reoperation of relay A, relay EB is short-circuited, an operating circuit is completed for relay EM and transmission of the XY pulse is thereforeterm'inated. When relay EBureleases after its slowperiod; the XY frequency is re-applied to line, while relay 6 EM is short-circuited. On the release of relay EM the second XY pulse is terminated. Relays A and B remain held, while relay SP proceeds to release slowly and the outgoing equipment is now in a condition awaiting the next dialled digit.

At the incoming end the first XY pulse releases relays DCC and AA, whereupon relay EBB is operated. At the end of the XY pulse, relays DCC and AA re-operate, whereupon relay EBB is short-circuited and relay EMM is energised. On reception of the second XY .pulse, relays DCC and AA again release and relay MC is operated. Relay MC in operating brings up relay SG but does not bring-up relay DZ in this instance, since relay DCC is not now operated. At the termination of the second XY pulse relays DCC and AA re-operate and relays M and PD are brought up, while relay EBB is short-circuited and relay EMM held. On the release of relay EBB, relay EMM is short-circuited and an output break period is initiated, while the circuit of relay M is opened and this relay commences to release slowly. On release of relay M the output break is terminated and relays PD and SG are released. Thus, in response to digit 1 the two XL frequency pulses received are absorbed at the incoming end and a single supplementary D. C. impulse is locally generated.

Relay I serves in known manner to disconnect the bothway terminating resistance YE from across the lines when the called subscriber answers.

With. regard to the release lags of certain of the relays at the outgoing and incoming ends relay. EB at the outgoing end has a minimum release lag of 50 m. s. so as to ensure that it will remain held during dialling at all speeds over a range of 7-12 I. P. S. Relay EM has a release lag of -150 m. s. when short-circuited by contacts Al so as to enable it to hold on dialled impulses, while it has a release lag of 60-90 m. s. when short-circuited over contacts EB! and resistance YA to ensure that the locally generated XY pulse will be of satisfactory duration.

At the incoming end relay EBB has a minimum release lag of 50 m. s. to enable it tohold during dialling, while it has a maximum release lag of '75 m. s. to ensure that the value of the output D. C. make period which is terminated by the release of relay EBB at contacts EBB2 shall not exceed a suitable value. Relay EMM has a release lag of 100-150 m. s. when short-circuited to enable it to hold during dialling, while relay M has a release lag of 60-90 m. s. to ensure that the D. C. break period generated at the incoming end shall be of satisfactory duration. Relay MC has an operate lag of 30-45 m. s. and relay CC has a release lag of -180 m. s. to prevent false preparation of the outgoing D. C. impulsing circuit by either spurious or non-dialling V. F. signals.

On receipt of a signal of XY frequency, relays DCCand AA are released and relay CC commences to release slowly and relay EBB is operated. If the signal persists for too long a time, as would be the case for long supervisory XY frequency signals in a V. F. signalling system employing compound frequency supervisory signals, relay CC releases after its slow period of 120-180 m. s. and disconnects relay EBB and operates relay SG to split the transmission path. On the termination of an XY frequency signal of proper duration, however, relays DCC and AA ramp-errata relay CC holds and relay EBB is short-circuited and rela EMM is operated If now the interval between the first XY frequency and a subsequent X or XY frequency is sufficiently great for relays EBB and EMM to release slowly in turn, it would be necessary for an XY frequency to be again received to re-prepare the circuit as an X frequency alone will not cause the release of relay AA. If however, the X or XY frequency follows after a normal interval, relay AA will be released in time to hold relay EBB and relay EMM will be shorted-circuited while a circuit will also be completed for relay MC. This relay is made slow-to-operate to ensure that it will only operate if a proper X or XY signal is received, i. e. a signal exceeding its 30-45 m. s. slow-to-operate lag. If the X or XY signal is sufiiciently long to operate relay MC, the circuit operation sequence follows in the manner already described.

We claim:

1. In a telephone system, a first line over which speech currents and series of direct current impulses representing digits are at times received, second and third lines associated with said first line so as to form a speech signal transmission channel, means responsive to a series of direct current impulses received over said first line for transmitting a corresponding series of voice frequency impulses over said second line, the number of said voice frequency impulses diifering from the number of said direct current impulses in a predetermined manner and the nature of certain of said voice frequency impulses, occupying particular positions in the series thereof, being different than the other voice frequency impulses included therein, and means responsive to said series of voice frequency impulses transmitted over said second line for transmitting a corresponding series of direct current impulses over said third line, whereby the risk of transmitting false direct current impulses over said third line in response to speech currents received over said first line is reduced.

2. A telephone system as claimed in claim 1 wherein the first and last voice frequency impulses in the series transmitted over said second line by said first means comprise a plurality of frequencies and the intermediate voice frequency impulses comprise a single frequency.

3. A telephone system as claimed in claim 1 wherein said last means includes means operated to disassociate said second and third lines so as to disable the speech signal transmission path while impulses are being repeated therebetween.

4. In a telephone system; a first line over which series of direct current impulses representing digits are at times received; a second line; means responsive to a series of direct current impulses received over said first line for transmitting a corresponding series of voice frequency impulses over said second line; the number of said voice frequency impulses varying in accordance with, but differing from, the number of said direct current impulses; a third line; and means responsive to said series of voice frequency impulses transmitted over said second line for transmitting a series of direct current impulses, equal in number to said first series, over said third line, the number of said voice frequency impulses in the series transmitted over said second line by said first means being one greater than the number of direct current impulses in the series received over said first line.

5. In a telephone system, a first line over which series of direct current impulses are at times received, a second line, means responsive to the first impulse of a series of direct current impulses received over said first line for transmitting a composite voice frequency impulse over said second line, means responsive to each succeeding direct currentimpulse in the received series for transmitting a corresponding voice frequency impulse consisting of a single frequency over said second line, and means responsive to the termination of said received series of direct current impulses for transmitting a further composite voice frequency impulse over said second line.

6. In a telephone system, a first line over which series of direct current impulses are at times received, a second line, means responsive to the first impulse of a series of direct current impulses received over said first line for transmitting a plural frequency alternating current impulse over said second line, means responsive to each succeeding direct current impulse in the received series for transmitting a corresponding single frequency alternating current impulse over said second line, and means responsive to the termination of said received series of direct current impulses for transmitting a further plural frequency alternating current impulse over said second line.

7. In a telephone system, a first line, means for transmitting series of voice frequency impulses representing digits over said first line, the first and last impulses of each series comprising a plurality of frequencies and the intermediate impulses comprising a single frequency, a second line, and means responsive to a series of said voice frequency impulses received over said first line for transmitting a corresponding series of direct current impulses over said second line, the number of direct current impulses in the series thereof being one less than the number of voice frequency impulses in the received series.

8. In a telephone system, a first line over which series of voice frequency impulses representing digits are at times received, the first and last impulses of each series comprising a plurality of frequencies and the intermediate impulses comprising a single frequency, a second line, means responsive to the first impulse of a series of said voice frequency impulses received over said first line for preparing to repeat succeeding impulses in the received series as direct current impulses over said second line, and means responsive to succeeding impulses in the series received over said first line for repeating corresponding direct current impulses over said second line.

9. A telephone system as claimed in claim 8 including means responsive to the termination of said series of voice frequency impulses received over said first line for transmitting a further direct current impulse over said second line.

10. In a telephone system, a first line over which series of direct current impulses are at times received, a second line, means responsive to the first impulse of a series of direct current impulses received over said first line for transmitting a composite voice frequency impulse over said second line, means responsive to each succeeding direct current impulse in the received series for transmitting a corresponding voice frequency impulse consisting of a single frequency over said second line, said first means being responsive to the termination of said series of direct current impulses to transmit a further com- 9 posite voice frequency impulse over said second line.

11. In a telephone system, a first line over which series of voice frequency impulses representing digits are at times received, the first and last impulse of each series comprising a plurality of frequencies and the intermediate impulses comprising a single frequency, means responsive to the first two impulses of a series of said voice frequency impulses received over said first line for preparing to repeat succeeding impulses in the received series as direct current impulses over said second line, means responsive to each impulse succeeding the second impulse in the received series for repeating corresponding direct current impulses over said second line, and means responsive to the termination of the received series of voice frequency impulses for transmitting 10 a further direct current impulse over said sec- 0nd line.

CHARLES GILLINGS. CHARLES EDMUND BELALE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

